Electrophysiological Recordings and Pharmacological Manipulation of the Neural Activity of the Prefrontal of Rats during Temporal Learning.
Temporal perception is essential for the adaptation and survival of several species, but its understanding is only at the beginning. Several brain regions and some types of neurons show activity correlated to temporal estimation tasks in trained animals. Less studied, however, is how these activities emerge with the learning. In part, the scarcity of results on this comes from the fact that learning in temporal estimation tasks usually takes many sessions to be observed. Recently, we adapted the training protocol on a DRRD task (Differential Reinforcement of Response Duration), reporting significant learning in the very first training session. Such a new protocol made it possible to monitor the evolution of the activity of individual neurons during learning. This study analyzed the neural activity in rats' prefrontal cortex while learning to estimate time in the DRRD task. For this, we adapted the behavioral procedure and the experimental apparatus to carry out electrophysiological studies. We recorded extracellular activity in five rats with implants of 32 electrode arrays in the medial prefrontal cortex. Besides, we used pharmacological experiments in which we inactivated the prefrontal cortex with muscimol. We also photo-stimulated the prefrontal cortex during the task using optogenetics. Our results indicate that cells in the medial prefrontal cortex encode temporal intervals, in agreement with the literature. Also, we observed that part of these cells alters their pattern of response during learning. However, using a classifier and regression methods to decode the time information, we noticed a reduction in the decoder performance resulting from learning. Our pharmacological studies suggested that the prefrontal cortex seems to have an essential role during learning, but not in the expression of behavior. Finally, the optogenetic stimulation experiments showed results similar to those of prefrontal cortex inactivation.